This invention relates to an oil seal structure in an automatic transmission.
In an automatic transmission, rotation generated by an engine is transmitted by way of a torque converter to a speed-changer, changed in speed in the speed-changer, and transmitted to drive wheels. The speed changer includes a number of gear elements and a number of different speed stages are achieved by selectively engaging and disengaging frictional engagement elements, such as clutches and brakes, which control rotation of the gear elements.
A brake is used to stop the rotation of a rotary gear element, and has one set of plates (outer plates) splined to the case of the automatic transmission, and another set of plates (inner plates) inter-leaved with the outer plates and connected to the rotary gear element through a splined connection. A hydraulic servo operates to engage the brake by pressing the outer plates and the inner plates together.
FIG. 2 is an enlarged view of a conventional seal, and FIG. 3 is a sectional view of a portion of a conventional automatic transmission. In FIG. 3, B2 is a second brake; F1 is a one-way clutch; 11 is an automatic transmission case; 12 is an output shaft; 16 is a brake hub, which is a rotary member constituting the outer race of the one-way clutch F1; and 17 is a sun gear shaft constituting the inner race of the one-way clutch F1.
The second brake B2 has a plurality of outer side thin plates 14 splined to the automatic transmission case 11, a plurality of inner side thin plates 15 disposed facing the outer side thin plates 14 and splined to the brake hub 16, and a hydraulic servo 21 for pressing the outer side thin plates 14 and the inner side thin plates 15 together. The hydraulic servo 21 is made up of an outer drum 22 having a C-shaped cross-section, an inner drum 23 fixed to the outer drum 22, a piston 24 slidably disposed between the outer drum 22 and the inner drum 23, and a return spring 26 for retracting the piston 24. The outer drum 22 is fixed in the automatic transmission case 11 through its peripheral component 36 which at one end abuts a snap ring 38 fixed to the automatic transmission case 11 and at its other end abuts a step 39 formed in the automatic transmission case 11. The outer drum 22 and the inner drum 23 together form the cylinder of the hydraulic servo 21.
An oil chamber 25 is formed between the outer drum 22, the inner drum 23 and the piston 24, and when oil is supplied into the oil chamber 25 the piston 24 is made to advance (move to the left in FIG. 3) to press together the outer side thin plates 14 and the inner side thin plates 15 and to thereby create a frictional force which serves to stop rotation of the inner side thin plates 15. In this way, the second brake B2 is engaged.
On the other hand, when oil is drained from the oil chamber 25, the piston 24 is caused by the urging force of the return spring 26 to retract (move to the right in FIG. 3) and the outer side thin plates 14 and the inner side thin plates 15 move apart. In this way, the second brake B2 is released.
A cylindrical connecting pipe 31 is disposed in a wall 28 of the automatic transmission case 11 to provide fluid communication between an oil hole 33 formed in the outer peripheral component 36 of the outer drum 22, and an oil passage 32 in this connecting pipe 31. Oil from a valve body (not shown) is supplied to the oil chamber 25 through the oil passage 32 and the oil hole 33.
Also, so that oil supplied through the oil passage 32 does not leak from between the connecting pipe 31 and the outer peripheral component 36, a cylindrical rubber seal member 37 is disposed abutting the end of the connecting pipe 31. Because the connecting pipe 31 being pressed against the outer peripheral component 36 through the seal member 37, the seal member 37 is compressed and a seal is formed owing to the elasticity of the seal member 37 (see Japanese Unexamined Patent Publication No. S.61-41058).
However, in the conventional automatic transmission described above, when it is necessary to axially extend the outer peripheral component 36 of the outer drum 22 along the inner surface of the automatic transmission case 11 to allow the outer side thin plates 14 to be splined to the outer peripheral component 36, the outer drum 22 functions to receive the reaction force arising on engagement of the second brake B2 as well as functioning as part of the hydraulic servo 21. Consequently, along with engagement and disengagement of the second brake B2, the outer drum 22 moves slightly, within a predetermined range, in the circumferential direction.
FIG. 2 shows the wall 28 of the automatic transmission case 11 (FIG. 3), the oil passage 32, the oil hole 33, the outer peripheral component 36 of the outer drum 22, and the seal member 37. Oil from the valve body (not shown) is supplied into the oil chamber 25 through the oil passage 32 and the oil hole 33. When the outer drum 22 moves slightly in the direction of the arrow A, with engagement and disengagement of the second brake B2, a tip portion 41 of the seal member 37 sometimes enters the gap between the wall part 28 and the outer peripheral part 36 and suffers damage.